U.S. Pat. No. 3,513,795 discloses a sewing head of the aforementioned type, the underarm of which carries a tubular stud arranged tiltably about an axis in the underarm, so that the tubular stud can be submersed into the underarm. Thus, it is possible to swing out a workholder, i.e. a carrier for a workpiece to be sewn out of the area of stitch formation. With this embodiment areas of obstacle of a thickness of only some millimeters (approximately up to 5 mm) as seen from the direction of the needle can be overbridged. At thicker obstacles it would be necessary to extend the size of the tubular stud, which would lead to difficulties at the actual process of stitch formation.
U.S. Pat. No. 361,426 discloses a sewing machine having an arm tiltable about an axis, in which the axis of the armshaft and the axis of a drive shaft pivoted in a standard cross each other. Moreover, the armshaft and the drive shaft are operably connected by bevel gears. Due to this development a construction is achieved, which is extraordinarily sensitive against tolerances.
Furthermore, sewing machines of the applicant are known the arm of which is upwards tiltable, i.e. about an axis, which is arranged in the sewing plane. Such sewing machines have workholders or carriers for a workpiece provided with areas of obstacles. Due to these areas of obstacles the clearance between the tip of the needle and the carrier for the workpiece is not sufficient to overcome such areas of obstacles when the needle is positioned in its upper dead center. Such sewing machines are provided with a drive connection of a 1 to 1 transmitting ratio between the armshaft pivoted in the arm and the hook driving shaft pivoted in the underarm. In order to keep the timing belt in a positive connection with the timing belt pulleys as the arm is tilted up, there are provided timing belt securing means. The maintaining of this positive connection between the timing belt and the timing belt pulleys is necessary in order to maintain the phase relation or the angular relation respectively between the armshaft and the hook driving shaft, which is essential for the stitch formation.